Dibble Creek IA 01-TRK-202

mouth (S34 T95N R7W Fayette Co.) to confluence with unnamed tributary in S27 T95N R7W Fayette Co.

Open Data Collection Period Modal

For purposes of developing stream/river water quality assessments for integrated reporting, three years of water quality data are typically used for both conventional pollutant parameters (e.g., indicator bacteria) and the less frequently monitored toxic parameters (e.g., toxic metals). Since the 2004 IR cycle, DNR has used a three-year data gathering period for streams, rivers, and beaches. For most assessments, the use of three years of data increases the number of samples upon which the decision on use support is based and helps address the problem of weather-related year-to-year fluctuations in water quality.

Due to the lower sampling frequency in Iowa’s ambient lake, biological, fish kill, and fish tissue monitoring programs, five years of data are used for developing IR assessments and for identifying Section 303(d) listings.

Data Type	Data Timeframe
Beach Sampling Data	CY 2012 - 2014
Stream/River Water Quality Data	CY 2012 - 2014
Lake Water Quality Data	CY 2010 - 2014
Biological Sampling Data	CY 2010 - 2014*
Fish Kill Data	CY 2010 - 2014
Fish Tissue Sampling Data	CY 2010 - 2014
Continuous Dissolved Oxygen Sampling Data	CY 2010 - 2014
*Biological sites sampled in both 2009 and 2013 were also assessed.

Open Segment Map
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Cycle: 2016
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown
Created: 5/5/2016 3:57:17 PM
Updated: 9/29/2016 8:04:37 AM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

5p - Impairment occurs on a waterbody with a presumptive A1 or B(WW1) use.

Cause Magnitude

Moderate

Status

New

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2016

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Watershed project monitoring

TMDL Priority

Tier III

Class BWW2

Aquatic Life - Warm Water Type 2

Fully Supported

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” (IR 5p) due to levels of indicator bacteria that exceed Iowa water quality criteria. This is a new impairment for this stream segment. The Class B(WW2) aquatic life uses are assessed (monitored) as “fully supported” (IR 2a) The source of data for this assessment is the results of monitoring from April 2012 to September 2014 at station DIB10 (Dibble Creek at Union Street (STORET station 15330004).

Assessment Explanation

The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the samples collected during the recreational season of 2012 (68 orgs/100 ml) and the recreation season of 2014 (40 orgs/100 ml) were both well below the Class A1 criterion of 126 orgs/100 ml. The geometric mean for the 2013 recreation season (1,714 orgs/100 ml) was well above this criterion. Six of the 16 samples collected during the 2012-2014 recreation season (38%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a geometric mean exceeds the 126 orgs/100 ml criterion, the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Until the 2016 assessment/listing cycle, this was one of the few warmwater steams in Iowa to have been monitored for indicator bacteria where the results indicated "full support" of the Class A1 uses.

The Class B(WW2) aquatic life uses are assessed (monitored) as “fully supported.” No violations of Class B(WW2) water quality criteria for ammonia (eight samples), dissolved oxygen (17 samples), pH (14 samples), temperature (17 samples) or chloride (11 samples) occurred in results of monitoring from April 2012 to September 2014.

Monitoring and Methods

Assessment Key Dates

4/4/2012

Fixed Monitoring Start Date

9/3/2014

Fixed Monitoring End Date

Methods

240

Non-fixed station physical/chemical (conventional + toxicants)

420

Indicator bacteria monitoring